Q&A on Chronic Wasting Disease

Chronic wasting disease (CWD) is a fatal neurological (brain and nervous system) disease found in deer, elk, caribou, and moose (cervids) populations in certain geographical locations in North America. CWD is caused by a mutant protein, called a prion. Learn more about the disease...

First recognized in the 1960s, it was diagnosed in free-ranging deer and elk in northeastern Colorado. The disease was then detected in wild deer in adjacent southeastern Wyoming and Nebraska, and in captive deer and elk in Colorado, Kansas, Montana, Nebraska, Oklahoma, Saskatchewan, and South Dakota.

Since that time, CWD has been spread eastward across the Mississippi River by the captive deer industry. Michigan found its first case of CWD in a captive deer herd in 2008. The disease was discovered in Oneida County, New York, in 2005 in a captive deer herd and two free-ranging deer nearby. Intensive lethal sampling of free-ranging deer in the area since that time has discovered no more infected deer.

The occurrences of deer herds experiencing CWD are relatively limited in geographic distribution throughout North America. However, CWD continues to spread to new locations as well as to areas around established disease areas.

Examinations of wild deer and elk where CWD has been found indicate about 1 to 25 percent or more of the animals can be infected. Captive facilities, where animals are fenced inside an area and tend to be in close physical contact, have an infection rate as high as 80 percent or more.

CWD has not been found in Vermont. The department sampled 400 hunter-harvested deer each year from 2002 to 2009. This level of sampling would detect CWD at a prevalence rate of 1 percent. All wild ungulates exhibiting symptoms similar to CWD have been euthanized and tested and no infected deer have been found.

The department also asks Vermonters keep a watchful eye for signs of this illness in free-ranging deer and moose. Biologists and wardens respond to several calls about sick deer every year, and these calls make an important contribution to disease monitoring efforts.

The Fish and Wildlife Board adopted a carcass importation rule for hunter-harvested cervids taken outside Vermont's borders. Only certain parts of the animal (such as the meat and skinned hide) may be brought into Vermont if the cervid was taken in a state or province that has had CWD.

The department maintains a list of previously infected states and provinces on the website and in the annual law digest. To legally import harvested deer, moose, or elk into Vermont, it is important to know what states and provinces have had infected animals.

The Board adopted a rule that bans baiting and feeding of deer - practices that could expose more deer to the disease.

Captive deer hunting facilities are under the jurisdiction of the Fish & Wildlife Department with greater enforcement capability to see that such facilities follow disease prevention and testing regulations.

The department tries to maintain free-ranging deer densities at less than 20 deer per square-mile by using hunters to harvest enough adult female deer annually. Having relatively low deer densities (compared to other southern and mid-western states) may prevent the disease from spreading rapidly if it gets here. It will also allow the department to eradicate the disease when it is initially found and before it becomes well established.

The World Health Organization (WHO) says there is no scientific evidence CWD can infect humans. However, WHO also suggests no part of a deer or elk with evidence of CWD should be eaten by people or other animals. In states where CWD is found, hunters are asked to dress the carcass without cutting the spinal cord, brain, eyes, lymph nodes, and tonsils.

Until a reliable conclusion can be drawn, the safest approach would be to not eat deer meat from animals appearing sick and from regions of the country where CWD is known to occur.

According to public health (Centers for Disease Control, World Health Organization) and animal health officials, data available to date indicate that chronic wasting disease is not currently known to be naturally transmitted to humans, or to animals other than the deer family. Data from recent molecular studies provide quantitative evidence of the apparent difficulty of cross-species transmission.

CWD is still not known to have infected any humans, but the mutant protein has been shown to have adaptive potential, so caution is still appropriate. As a general precaution, public health officials recommend that people avoid contact with deer, elk, or any other wild animal that appears sick.

Although there's no evidence that CWD can be naturally transmitted to domestic livestock, CWD is similar in some respects to two livestock diseases:

Scrapie, which affects domestic sheep and goats worldwide and has been recognized for over 200 years

Bovine spongiform encephalopathy (BSE), which is a more recent disease of cattle in the United Kingdom and Europe.

Despite some similarities, there is no evidence suggesting either scrapie or BSE are caused by contact with wild deer or elk, or that wild deer or elk can contract either scrapie or BSE in countries where these diseases occur.

To test for CWD a small piece of brain tissue is examined under a microscope for the presence of the causative prions. A list of laboratories certified by the United States Department of Agriculture to test deer and elk tissues for the presence of chronic wasting disease can be found here.

There is hope because New York may have managed to do just that. Many states have tried and failed to eradicate CWD when it was found.

Many southern and mid-western states have deer densities ranging from 50 to 100 deer per square-mile. In such situations, the disease can be expected to spread rapidly, making it difficult to contain or eradicate CWD before it becomes established in more than 1 percent of the population.

Wisconsin spent millions of dollars trying to eradicate the disease by depopulating free-ranging deer, but failed. Scientific research later indicated that CWD was present in Wisconsin over a decade before it was discovered, so disease eradication efforts there were just too late.

Other states have not attempted to eradicate CWD when it was first recognized. These states have deer densities of over 50 deer per square-mile, making disease eradication unlikely. Management decisions to depopulate free-ranging deer are also politically unpopular.

The department has a CWD Strategic Management and Response Plan. The scientific consensus is that when CWD is first detected in a new area, disease eradication should be attempted if it is deemed possible.

Eradication of CWD can be achieved if free-ranging deer can be depopulated to 0 to 5 deer per square-mile for a period of at least 5 years in an area within about 10 miles of the location where the initial infected animal was found. That is an area of about 300 square miles. With few or no deer to spread the disease, the infectious prions that cause CWD die after a few years.

Disease eradication is possible in Vermont because:

Local deer densities in Vermont are relatively low and range from 5 to 25 deer per square mile.

Depopulating winter concentrations of deer would be relatively easy to do and would effectively cover larger areas.

CWD should be less than 1 percent prevalent in the population when it is first detected because a sick deer would be relatively visible in Vermont. This is why it’s important for Vermonters to report seeing sick deer.

There is just one chance to eradicate CWD when it is first discovered, and it’s the department's legal duty to see that the health of Vermont's deer herd is protected. It may not be a popular action to take, but it will be necessary to try to eradicate the disease for the sake of the deer and deer hunting tradition.